Reorganize to split util

1 files changed, 103 insertions, 0 deletions

diff --git a/src/util/decode_character_reference.rs b/src/util/decode_character_reference.rs
new file mode 100644
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--- /dev/null
+++ b/src/util/decode_character_reference.rs
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+//! Utilities to decode character references.
+
+use crate::constant::{CHARACTER_REFERENCE_NAMES, CHARACTER_REFERENCE_VALUES};
+
+/// Decode named character references.
+///
+/// Turn the name coming from a named character reference (without the `&` or
+/// `;`) into a string.
+/// This looks the given string up in [`CHARACTER_REFERENCE_NAMES`][] and then
+/// takes the corresponding value from [`CHARACTER_REFERENCE_VALUES`][].
+///
+/// The result is `String` instead of `char` because named character references
+/// can expand into multiple characters.
+///
+/// ## Examples
+///
+/// ```rust ignore
+/// use micromark::util::character_reference::decode_named;
+///
+/// assert_eq!(decode_named("amp"), "&");
+/// assert_eq!(decode_named("AElig"), "Æ");
+/// assert_eq!(decode_named("aelig"), "æ");
+/// ```
+///
+/// ## Panics
+///
+/// This function panics if a name not in [`CHARACTER_REFERENCE_NAMES`][] is
+/// given.
+/// It is expected that figuring out whether a name is allowed is handled in
+/// the parser.
+/// When `micromark` is used, this function never panics.
+///
+/// ## References
+///
+/// *   [`wooorm/decode-named-character-reference`](https://github.com/wooorm/decode-named-character-reference)
+/// *   [*§ 2.5 Entity and numeric character references* in `CommonMark`](https://spec.commonmark.org/0.30/#entity-and-numeric-character-references)
+pub fn decode_named(value: &str) -> String {
+    let position = CHARACTER_REFERENCE_NAMES.iter().position(|&x| x == value);
+    if let Some(index) = position {
+        CHARACTER_REFERENCE_VALUES[index].to_string()
+    } else {
+        unreachable!("expected valid `name`")
+    }
+}
+
+/// Decode numeric character references.
+///
+/// Turn the number (in string form as either hexadecimal or decimal) coming
+/// from a numeric character reference into a character.
+/// Whether the base of the string form is `10` (decimal) or `16` (hexadecimal)
+/// must be passed as the `radix` parameter.
+///
+/// This returns the `char` associated with that number or a replacement
+/// character for C0 control characters (except for ASCII whitespace), C1
+/// control characters, lone surrogates, noncharacters, and out of range
+/// characters.
+///
+/// ## Examples
+///
+/// ```rust ignore
+/// use micromark::util::character_reference::decode_numeric;
+///
+/// assert_eq!(decode_numeric("123", 10), '{');
+/// assert_eq!(decode_numeric("9", 16), '\t');
+/// assert_eq!(decode_numeric("0", 10), '�'); // Not allowed.
+/// ```
+///
+/// ## Panics
+///
+/// This function panics if a invalid string or an out of bounds valid string
+/// is given.
+/// It is expected that figuring out whether a number is allowed is handled in
+/// the parser.
+/// When `micromark` is used, this function never panics.
+///
+/// ## References
+///
+/// *   [`micromark-util-decode-numeric-character-reference` in `micromark`](https://github.com/micromark/micromark/tree/main/packages/micromark-util-decode-numeric-character-reference)
+/// *   [*§ 2.5 Entity and numeric character references* in `CommonMark`](https://spec.commonmark.org/0.30/#entity-and-numeric-character-references)
+pub fn decode_numeric(value: &str, radix: u32) -> char {
+    let code = u32::from_str_radix(value, radix).expect("expected `value` to be an int");
+
+    if
+    // C0 except for HT, LF, FF, CR, space
+    code < 0x09 ||
+    code == 0x0B ||
+    (code > 0x0D && code < 0x20) ||
+    // Control character (DEL) of the basic block and C1 controls.
+    (code > 0x7E && code < 0xA0) ||
+    // Lone high surrogates and low surrogates.
+    (code > 0xd7ff && code < 0xe000) ||
+    // Noncharacters.
+    (code > 0xfdcf && code < 0xfdf0) ||
+    ((code & 0xffff) == 0xffff) ||
+    ((code & 0xffff) == 0xfffe) ||
+    // Out of range
+    code > 0x0010_ffff
+    {
+        '�'
+    } else {
+        char::from_u32(code).expect("expected valid `code`")
+    }
+}